Originally Posted by
RoadLight
Hi hcgaloi,
When a chain needs to be replaced because it has stretched, you should change the cassette also. Why? Because the teeth of the cogs will have been worn lopsided by the stretched chain and mounting a new chain to a cassette with irregularly worn teeth will cause a new set of problems like decreased shifting performance and easier chain slips. This is why many experienced bike mechanics will tell you that cassettes should be considered as "consumables" the same as the chain.
One way to delay replacing the cassette is to replace the chain a little early. Since chains are usually cheaper than a comparable-quality cassette, you save money in the long run. This may be what your LBS is thinking. So the mechanic's advice might be correct.
Kind regards, RoadLight
If you replace a chain within specs, you'll get 2-3 chains per cassette. Plus, you'll know if the cassette needs changing because it will jump and/or shift poorly when a new chain is put on. The bike won't be unrideable, just annoying. Take it for a spin, see if it's running OK or not, and go from there.
Replacing a cassette routinely with a chain is just a waste.
As for the OP: you have three options: (1) Just replace the chain as advised (2) ask the tech why he's advising it and ask him to show you how he measured it (2a): if he uses a ruler to measure a taught chain and gets 1/16" elongation as described, go ahead and change it, otherwise (3): get yourself an accurate ruler and simply measure the chain yourself. If it is 1/16" enlongated, replace it. If not, don't.
I measure chains by taking them off and hanging from a nail and measuring 12 links, rivet to rivet. Actually, I have an old chain that is 1/16" long, so I just hang them from the same nail and see where the rivets line up. If they're equal, replace. If the chain is shorter than the old chain, I run it for a while longer. But I use quick links so this is easy.
I get 3+ chains per cassette.